Process and apparatus for drying photographic prints



R. B. KEMP, JR

PROCESS AND APPARATUS FOR DRYING PHOTOGRAPHIC PRINTS 2 Sheets-Sheet 1 Filed Aug. 8, 1967 R. B. KEMP, JR

' Oct. 8, 1968 PROCESS AND APPARATUS FOR DRYING PHOTOGRAPHIC PRINTS 2 Sheets-Sheet 2 Filed Aug. 8, 1967 INVENTOR. ROBERT E. Kzz-malfiz.

BYW 4 $130 ATTORNEYS:

United States Patent 3,404,463 PROCESS AND APPARATUS FOR DRYING PHOTOGRAPHIC PRINTS Robert B. Kemp, Jr., 4026 S. Tryon St., Charlotte, N.C. 28210 Filed Aug. 8, 1067, Ser. No. 659,060 Claims. (Cl. 34-23) ABSTRACT OF THE DISCLOSURE Process and apparatus for the high-speed drying of photographic paper prints without damaging their emulsion surfaces, wherein moist prints are continuously moved through a drying zone where they are sequentially contacted with moist steam and relatively dry heated air currents, and wherein the initial contact of the prints with the dry air currents is at a temperature below the steam temperature, and the prints are thereafter contacted'by progressively warmer and dryer air currents to reduce the moisture content of the prints to a desired level.

The present invention relates to a process and apparatus for the high-speed drying of photographic prints, and more specifically to such a process and apparatus wherein a web of photographic paper prints having an emulsion coating thereon is moved continuously through a drying zone where the prints are sequentially contacted with moist steam and dry air to effectively dry the prints at a rapid rate without damage to the delicate emulsion surfaces of the prints.

In the continuous drying of photographic paper prints, it has been customary, after their wet processing, to pass a wet web or roll of paper prints into engagement with the smooth peripheral surface of a large diameter, internally heated drum which is rotated at a relatively slow speed while the heat from the drum evaporates the water and other solvents from the paper. Although drum drying is widely used, it has several disadvantages. Since the temperature of the surface of the drum must be maintained relatively low to avoid damaging the delicate emulsion surfaces of the prints, the prints must remain on the drum for an appreciable length of the time to insure proper drying. This necessitates the employment of low drum speeds and results in a low linear output of the prints from the dryer, generally at or below about six and a half feet per minute in the conventional size drums in use toda B cause of the nature of the chemicals in the gelatin base, emulsion coating on one surface or face of the prints, the paper prints have a strong tendencyto curl about their edges, due to contraction of the emulsion, until the moisture content of the paper drops below a certain level. For this reason, it is necessary to insure that the prints are firmly held against the drums surface during drying. In such cases, the moisture which is trapped between the peripheral suiface of the drum and the contacting surface of the paper causes drying spots to appear on the emulsion side of the prints which detract from the appearance of the finished photograph.

In an attempt to alleviate some of these problems, it has been suggested to dry photographic prints by conveying them between endless belts or on endles chains through a hot air drying zone. However, these dryers also have several disadvantages. Becasue they must also utilize relatively low temperatures to avoid damaging the emulsion surfaces of the prints, the speed of the prints through the zones must be necessarily slow or the dryers excessively large to insure proper drying of the prints. In addition, the aforementioned curling tendency of the prints is a major problem in such dryers since the paper 3,404,463 Patented Oct. 8, 1968 prints are not kept at all times in contact with a smooth shape-retaining surface. Further, the conveyor belts and the surfaces over which the prints travel often scratch, crease or otherwise damage the prints during their movement through the dryer. Additionally, in drying photographic prints, particularly color prints, the emulsion side of the prints becomes quite sticky or tacky at an intermediate point of the drying process making it highly desirable to avoid contacting the emulsion side of the prints with a relatively moving surface while this sticky or tacky condition exists. This is extremely difficult when the aforementioned endless belt and chain arrangements are utilized to dry the prints.

It is therefore an object of the present invention to overcome these and other disadvantages of the prior art drying apparatus by providing a high-speed drying apparatus wherein photographic paper prints, both black and white and color, may be dried to provide a finished product of excellent quality.

It is another object to provide a process for drying photographic prints in which prints can be dried at a high rate of speed and output without undesired curling of the edges of the prints and without damage to the emulsion surfaces thereof.

It is another object to provide a high-speed dryer for photographic print materials which is of relatively economical construction and operation, and wherein a rapidly moving web of the photographic prints may be dried under controlled temperature and humidity conditions to produce excellent photographic products.

The objects of this invention are accomplished by contacting continuously moving wet photographic paper prints with moist steam for a sufficient period of time to raise the temperature of interior of the prints and force migration of the moisture outwardly therefrom without appreciably drying their emulsion surfaces, and thereafter passing the heated moving prints into contact with relatively dry heated air wherein the temperature of the prints is gradually raised to reduce the moisture of the paper prints to the desired level of dryness. By directing the.

heated air currents generally counter to the direction of movement of the prints through the zone, the prints can be contacted by progressively warmer and dryer air currents to uniformly remove the moisture therefrom.

Although superheated steam has been used in the paper industry to dry paper during its production, it has not heretofore been thought possible to dry photographic prints by the use of steam, since the emulsion surfaces of prints, particularly color prints, contain chemicals that are highly soluble in water. Additionally, the emulsion coatings are easly damaged at temperatures above about 250 F., and temperatures above this point are generally deemed necessary to afford any substantial drying by the use of steam.

Surprisingly, however, I have found that by treating moving prints with moist steam of a relatively low temperature and for a relatively short period of time during the initial stage of the drying process, and thereafter contacting the prints with dry heated air under controlled temperature conditions, the photographic prints may be rapidly and uniformly dried without damage to the exterior emulsion surfaces and without appreciable curling of the prints during the drying process.

To obtain maximum heat transfer during minimum contact of the prints with the steam, the steam is impinged directly against opposing surfaces of the moving prints to quickly raise their temperature while maintaining their outer surfaces in a relatively moist, porous condition. The prints are then immediately passed into contact with relatively dry heated air currents having an initial temperature which is lower than the temperature of 3 the treating steam. The air currents are passed generally counter to the direction of movement of the prints so that the prints are subject to drying by currents of progressively warmer and dryer air. Although it would appear that the prints could be dried more efficiently if steamtreated prints were subjected to an initial dry air temperature which is the same as or higher than the steam temperature. It has been found, however, that when as high or higher dry air temperatures are used immediately after steam treatment, the heated air tends to produce excessive curl in the moist paper as it travels through the dryer. Additionally, the sudden change in the moisture content of the heating medium at such temperature results in undesirable reticulation, or fracturing and wrinkling, of the gelatin-base emulsion coating on the prints. Therefore, it has been found desirable to subject the steam-treated paper to a dry air temperature initially lower, generally by about F. to F., than that of the steam temperature.

By utilizing the sequential steam-dry air treatment of the prints during the drying process, it has been found that the prints can be more rapidly handled and moved through the drying apparatus without damage to their emulsion surfaces. In this respect, I have found that one or more webs of prints may be continuously moved over relatively small diameter guide rollers of the dryer at linear speeds of more than twice the speed of the conventional continuous drum dryers without damage to the prints.

The temperatures of the steam and dry air drying mediums may be varied and depend to some extent on the speed at which the prints are moved through the contact zones of the drying process. As previously mentioned,

the steam temperature should be maintained below 250 F. to avoid damage to the gelatin-base emulsion surface of the prints. In like manner, the highest temperature of the dry air at the outlet end of the drying apparatus should be maintained below 250 F., and preferably below 240 F., in order to avoid objectionable curl of the paper and brittleness of the prints. In operation it has been found that dry prints of excellent quality can be obtained, at linear output speeds as high as twelve feet per minute, when the steam temperature is maintained between about 212 F. to 240 F. and the hottest dry air temperature is maintained at about 180 F. to 190 F.

The novel features and construction of the drying apparatus used to carry out the foregoing high-speed drying process may .best be explained and understood by reference to the accompanying drawings in which- FIGURE 1 is a front overall perspective view of the dryer;

FIGURE 2 is a back perspective view of the dryer as seen in FIGURE 1;

FIGURE 3 is an enlarged sectional view of the dryer taken along line 33 in FIGURE 1;

FIGURE 4 is a sectional view of the dryer taken along line 44 in FIGURE 3;

' FIGURE 5 is a fragmentary sectional view taken generally along line 5-5 in FIGURE 3 and showing the electrical heating unit located in the lower left portion f the dryer;

FIGURE 6 is a fragmentary perspective view of the steam distribution conduits located in the first treating compartment of the apparatus; and

FIGURES 7 and 8 are enlarged sectional views of vup- 'per and lower rotatable guide rollers, respectively, of the 4 7 thereof during operation of the drying apparatus. Located in a lower portion of the end wall 12 is a narrow opening 23 which serves as an inlet for introducing one or more webs W of wet photographic paper prints into the housing, and a similarly configured narrow opening 24 in the lower portion of the opposite end wall 14 of the housing serves as an outlet for the removal of the dry webs of prints therefrom. The walls of the housing may be constructed of suitable material, such as insulated sheet metal or the like, to insure minimum heat loss from the housing. Both the housing inlet 23 and outlet 24 have flexible strips of sealing elements 23a, 24a secured to their upper and lower edges which permit the passage of the webs W therethrough, but effectively aid in preventing heat loss from the enclosure housing during operation of the apparatus.

Positioned within the housing a spaced distance from the end wall 12 and extending generally parallel thereto is a partition wall 26 (FIGURE 3) which divides the housing into first and second treating compartments 28, 30. The partition wall has a narrow horizontally-extending opening 32 located in its lower portion to permit the passage of the webs of prints between the first and second treating compartments during their movement through the housing 10.

As best seen in FIGURE 3, one or more of the webs W of paper prints, containing evaporable solvents and moisture from previous wet processing steps, pass simultaneously through inlet 23 and are guided through the housing 10 from inlet to outlet therein by opposing sets 40, 42 of guide rollers 43, 44, respectively, which are mounted in generally parallel spaced alignment in the upper and lower portions of the housing 10 throughout its length. All of the rollers are rotatably mounted in suitable journal bearings 46 (FIGURES 7 and 8) which are suitably secured to the back wall 20 of the housing and bracket members 47 which are located inside the doors 22 of the housing. All of the rollers 43 in the upper set of rollers 40 are positively driven by suitable power means, such as electric motor 51 (FIGURE 2), which is drivingly connected to each of the rollers by an endless chain 48 and sprockets 49 which are mounted on the ends of roller shafts 50 (FIGURE 7) externally of the housing 10.

For convenience, the webs W of prints pass into and through the housing with their emulsion-coated sides or faces disposed upwardly, and are guided by sequential passage under and over the sets of rollers in a plurality of generally parallel reaches R extending throughout the first and second treating compartments of the housing. As best seen in FIGURES 7 and 8, the surfaces of the rollers 43 and 44 are of conventional crown construction, having raised portions 45 spaced along their peripheries to facilitate proper track of the webs thereover. Each roller 44 in the lower set 42 of rollers is mounted for free rotation and is coated with an antifriction coating 44a of polytetrafluoroethylene to avoid damage to the emulsion surfaces of the prints which contact the lower roller surfaces during their passage through the housing 10. By locating the support rollers only at the ends of the reaches R, the prints may be maintaind free of frictional contact with any surface throughout the major portions of the reaches, leaving the webs of prints well exposed for contact by heated air currents, as will be explained. Additionally, by moving the webs of prints by positive drive of the upper rollers 43, which contact the backs of the prints, while retaining the lower, coated rollers 44 freely rotatable for movement by the webs, minimal frictional contact of the emusion coatings of the prints can be achieved during the critical periods of drying when the emulsion coatings are most subject to damage by such contact.

The first treating compartment 28 of the housing 10 is provided with means for introducing live steam into the compartment which includes an elongate header conduit 52 (FIGURES 3 and 6) extending upwardly in the compartment and pairs of opposing horizontally disposed distributor conduits 56 communicating with the header conduit 52 at spaced intervals along its length. As best seen in FIGURE 6, each pair of distributor conduits 56 transversely straddle the first reach of the webs of prints passing through the treating compartment 28 and the inner sides of the conduits are provided with a plurality of inwardly directed orifices 59 to permit the impingementof plural streams or jets of live steam directly against opposing portions of the opposing faces of the moving webs of prints. In this manner, the hot moist steam can raise the temperature of the prints so as to initiate the migration of moisture outwardly from the interior portions of the .prints while maintaining the exterior portions in relatively moist porous condition. Direct impingement of the steam simultaneously against opposing portions of the opposite sides of the webs also provides optimum heat transfer from the steam to the prints as they pass through the first compartment.

The lower end of the header conduit 52 communicates with the end of an elongate steam line 60 (FIGURES 3 and 4) which extends throughout the lower portion of the second compartment 30 to provide a secondary heat source thereto, as will be explained. Steam is supplied to the steam line 60 and to the header conduit and distributor conduits from an external steam source S (FIGURE 2).

Located in the second treating compartment 30 between the partition wall 26 and the outlet end of the housing are a plurality of spaced, vertically-disposed plates 62 which are connected to the side walls of the housing and extend alternately from the bottom and top walls to define with the housing a sinuous passageway P for the flow of air currents through the second treating compartment. As best shown in FIGURE 3, the plates 62 are generally uniformly spaced throughout the length of the second compartment 30 to position at least two guide rollers, and corresponding reaches of the moving webs of prints, in each vertical section of the passageway defined by adjacent plates, partition wall 26, and end wall 14 of the housing.

In addition to the steam line 60, the second treating compartment 30 is provided with a primary source of dry heat, such as an electrical heating unit 64 (FIGURES 3 and 5) located in the lower end portion of the sinuous passageway P adjacent the housing outlet 24. The electrical heating unit 64 includes suitable controls 64a located on the exterior face of the housing wall 14 for regulating the heat output of the unit. Additionally, if desired, one or more thermostats (not shown) may be provided at suitable locations in the second compartment to automatically regulate the unit to maintain the compartment temperatures at a desired level.

Mounted on the top wall 16 of the housing 10 and communicating with an opening 70 into the upper end of the last section of the sinuous passageway P of the second treating compartment is an air blower 72 which cooperates with the electrical heating unit 64 to provide means for creating relatively dry heated air in the second treating compartment and for propelling the air in a stream through the sinuous passageway P from adjacent the housing outlet 24 to the partition wall opening 32 (note arrows A in FIGURE 3 Air currents, upon reaching the end of the passageway P adjacent the partition wall opening 32, pass through the opening and into the first treating compartment 28. Located in the top wall of the housing 10 and communicating with the upper end portion of the first treating compartment is an air vent 74 which serves to permit removal of the air currents and steam from the first treating compartment of the housing. The vent 74 may be provided with an adjustable cover 76 to further assist in regulation of the temperature and humidity conditions in the housing. By locating the partition wall opening 32 in the lower portion of the first treating compartment 28 and the air vent 74 in the upper portion thereof, air currents passing through the first treating compartment from the second treating compartment are permitted to move generally upwardly parallel to the moving reaches R of the web of prints in the compartment, thereby serving to quickly sweep the moist steam impinging against the faces of the prints from the treating compartment 28. In this manner, the moist steam is quickly removed from the emulsion surface of the webs of the prints after heat transfer, thereby avoiding possible damage to the emulsion coatings of the prints due to dissolution of the Watersoluble components therein by an excessively long contact with the moist steam. Additionally, in this respect, the pressure of air currents passing through the partition wall opening 32 is maintained so as to prevent substantial bleeding of any steam from the first treating compartment into the second, dry air treating compartment. By controlling the temperature of the moist steam and dry heat sources so as to maintain a lower temperature in the first section P of the sinuous passageway adjacent the partition wall 26 than the moist steam temperature in the first treating compartment 28, the moving webs of prints can be sequentially contacted with moist steam and relatively dry air currents to rapidly dry the prints without causing an undesired curling of the edges of the prints or otherwise damaging their emulsion coatings. Additionally, by passing the relatively dry heated air currents in a direction generally counter to the direction of movement of the webs of prints through the second treating compartment, the opposing faces of the prints can be subjected to progressively warmer and dryer air to insure uniform moisture removal from the prints while the opposing faces of the same remain unsupported and relatively free from contact with a relatively moving surface during their movement through the drying apparatus.

As will be appreciated from the foregoing discussion and detailed description of the drawings, the drying apparatus and process of the present invention permits high speed drying of moist webs of photographic paper prints by initial moist steam treatment of the moving prints, followed by contact with relatively dry heated air currents wherein the emulsion coatings on the prints during drying are maintained relatively free from contact with a surface of relative movement while the prints are uniformly dried to a desired moisture level without damage to the coatings.

In the drawings and specification there has been set forth a preferred embodiment of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being defined in the claims:

That which is claimed is:

1. A process for the high speed drying of moist photographic paper prints having an emulsion coating thereon and containing evaporable solvents, comprising the steps of:

(a) continuously moving the prints in a predetermined path through a confined heating zone;

(b) contacting opposing faces of the moving prints in a first portion of said heating zone with moist steam to raise the temperature of the prints to initiate the migration of moisture outwardly from the interior portions thereof and to maintain the outer portions of the prints in relatively moist, porous condition;

(c) thereafter contacting the moving prints in a second portion of said heating Zone with relatively dry heated air currents at a temperature below the temperature of the steam to aid in preventing curling of the prints, and

(d) thereafter contacting the moving prints in said second portion with progressively warmer and dryer air during their passage therethrough to reduce the moisture content of the prints to a desired level.

1 2. A process as defined in claim 1 wherein said moist steam is maintained at a temperature of between about 212 F. and 250 F.

1 3. A process as defined in claim 1 wherein said prints are in the form of a continuous web and the web is moved through said heating zone in a plurality of reaches, with the major portions of the reaches being free of contact with any surface to avoid damage to the emulsion coatings of the prints.

4. A process as defined in claim 1 wherein said moist steam in the first portion of the heating zone is directly impinged in a plurality of streams against opposed portions of said opposing faces of the moving prints to efiect rapid'heating of the prints; and including the step of passing air currents through said first portion of said heating zone and generally parallel to the moving faces of said prints to quickly remove the moist steam from said zone and thereby avoid dissolution of said coating surfaces of said prints by prolonged contact with the steam.

5. An apparatus for the high speed drying of a web of photographic paper prints having an emulsion coating on one surface thereof, comprising:

(a) an enclosure housing having a partition wall dividing said housing into first and second substantially closed treatment compartments, an inlet for the web of prints in said housing communicating with said first treating compartment and an outlet for the web of prints communicating with said second compartment, and an opening in said partition wall for passage of the web of prints between said first and second treating compartments;

(b) means in said second treating compartment defining an elongate sinuous passageway for the flow of air therethrough, said passageway extending from said partition wall opening to said housing outlet;

() means for longitudinally moving the web of photographic paper prints through said housing from said inlet to said outlet and for guiding said web in a plurality of generally parallel reaches through said first compartment and said sinuous passageway of said second compartment;

(d) steam heating means including means for introducing live steam in said first treating compartment for direct contact with the web of prints passing therethrough;

(e) additional heating means for creating relatively dry heated air into the end portion of said elongate passageway adjacent said housing outlet and for propelling said air in a stream through said sinuous passageway and said partition wall opening into said first compartment at a suificient velocity to substantially prevent the bleeding of steam from said first treating compartment into said second treating compartment through said partition wall opening, and

(f) a vent in said housing wall communicating with said first treating compartment for discharging said air and steam from said housing.

6. Apparatus as defined in claim 5 wherein said means defining said passageway for the flow of air includes a plurality of spaced parallel plates extending alternately from opposing walls of said housing to define a zigzag path through said second compartment for said air stream; and wherein said means for moving and guiding the web of prints through said housing includes a plurality of rotatable guide rollers spaced throughout said compartments to position at least two reaches of the web of prints between each of said spaced plates.

7. Apparatus as defined in claim 6 wherein the surfaces of all of said rotatable rollers which are adapted to contact the emulsion coatings on said prints are composed of polytetrafiuoroethylene, and wherein said rotatable rollers are located at the ends of said plurality of reaches and provide the sole support for said web of prints to permit the :web of prints to be free from contact with a surface over the major portions of the lengths of said reaches.

8. Apparatus as defined in claim 7 wherein said moving and guiding means for the web of prints further includes means for positively driving each of said rotatable rollers located at one set of corresponding ends of said plurality of reaches, and wherein the remaining rollers in said housing are freely rotatable for movement during contact with said web of prints passing thereabout.

9. Apparatus as defined in claim 5 wherein said means for introducing live steam into said first treating compartment includes conduit means in said first treating compartment for simultaneously directing a plurality of streams of steam directly against opposed portions of the opposing faces of the web of prints during its passage over one reach in said first treating compartment; and wherein said additional heating means includes a source of heat located adjacent said housing outlet and blower means located adjacent the end of said sinuous passageway for directing air currents over said heat source and through said passageway.

10. Apparatus as defined in claim 5 wherein said partition wall opening is located in a lower portion of said wall, said housing inlet and outlet are located in the lower portion of said housing, and said vent for discharging air and steam from said housing is located in the upper portion of said housing, whereby air currents passing through said first treating compartment are permitted maximum contact with said reaches of sheet material therein to sweep said steam from contact with the web of prints during its passage through said first treating compartment.

References Cited UNITED STATES PATENTS 2,772,486 12/1956 Johanson 34159 2,884,706 5/1959 Svavar et a1 34-159 XR 2,928,329 3/1960 Limbach 34-159 3,263,345 8/1966 Fleisher et a1. 34--159 KENNETH W. SPRAGUE, Primary Examiner. 

